Mechanical pipe couplings are used throughout a broad spectrum of industry, for example, in mining, petroleum extraction and refining, chemical production as well as in fire protection systems used in office buildings, warehouses, schools and the like. Mechanical couplings provide significant advantages over other methods of joining pipe elements together, for example, welding or brazing, in that they allow for the assembly of a fluid carrying piping network by relatively unskilled labor using simple tools. The term “pipe elements” is used herein to denote any pipe-like item or component having a pipe-like form. Pipe elements include pipe stock, pipe fittings such as elbows, caps and tees as well as fluid control components such as valves, reducers, strainers, restrictors, pressure regulators and the like.
FIG. 1 shows an example of a mechanical pipe coupling 10 according to the prior art. Coupling 10 comprises two (or more) segments 12 and 14 that are positionable straddling a sealing member 16 and pipe elements 18 and 20. Each coupling segment 12 and 14 has arcuate surfaces 22 and 24 that respectively engage the pipe elements 18 and 20 to secure them in end to end relation. In the example shown in FIG. 1, the arcuate surfaces 22 project radially inwardly and engage grooves 26 in the ends of the pipe elements. Other examples include pipe elements having smooth ends, flared ends or raised shoulders that are engaged by the couplings.
The sealing member 16 engages both pipe elements 18 and 20 and ensures a fluid-tight joint. Sealing member 16 is preferably a flexible elastomeric ring that is positioned within a cavity 28 within the coupling defined by a pair of sidewalls 30 and 32 attached to a back wall 34. Sealing member 16 is compressed into engagement with the pipe elements by contact with the sidewalls and back wall of the coupling segments 12 and 14 as the segments are drawn together to form the pipe joint.
As shown in FIGS. 2 and 3, coupling segments 12 and 14 may have angularly oriented surfaces 36 and 38 positioned at opposite ends. The slopes of the surfaces are oriented opposite to one another on each segment. When the surfaces on two segments are positioned in facing relation, as when the segments are straddling pipe elements 18 and 20, and the segments are drawn together, sliding engagement of the surfaces causes the segments to rotate in opposite directions relatively to one another about an axis 40 that is oriented substantially perpendicular to the longitudinal axis 42 of pipe elements 16 and 18. The relative rotation of the segments 12 and 14 is desirable because it forces the arcuate surfaces 22 and 24 into engagement with the side surfaces of grooves 26 in the pipe elements and adds rigidity to the joint about all axes, i.e., bending and torsion, as well as preventing axial expansion or contraction.
In addition to the angularly oriented surfaces described herein, there are other means for effecting relative rotation of the coupling segments, such as the crescent shaped protrusion interfitting within the crescent shaped groove as disclosed in U.S. Pat. No. 5,246,257, hereby incorporated by reference, or the use of offset apertures in attachment flanges as disclosed in U.S. Pat. No. 4,861,075, also hereby incorporated by reference.
To connect segments 12 and 14, each segment has connection members positioned at opposite ends of the segments. In the example illustrated in FIGS. 2 and 3, the connection members comprise projections 44 in the form of lugs that extend outwardly from the segments. The projections have apertures 46 that receive fasteners such as bolts 48 and nuts 50 which, when tightened, cause the segments 12 and 14 to be drawn toward one another.
While it is advantageous in certain circumstances to increase the rigidity of the joint by rotating the coupling segments about axis 40, this rotation of the segments deforms the sealing member 16 through its engagement with the sidewalls 30 and 32. It is preferable not to distort the shape of the sealing member through rotation of the segments.